[tex]\displaystyle\bf\\2)\\\\Cos\alpha Cos\Big(\frac{\pi }{2} -\alpha \Big)=Cos\alpha \cdot Sin\alpha =\frac{2Sin\alpha Cos\alpha }{2} =0,5Sin2\alpha \\\\\\4)\\\\Sin2\alpha +(Sin\alpha -Cos\alpha)^{2} =\\\\=2Sin\alpha Cos\alpha +Sin^{2} \alpha -2Sin\alpha Cos\alpha +Cos^{2} \alpha =\\\\=Sin^{2} \alpha +Cos^{2} \alpha =1[/tex]